The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders.
The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae.
Spondylolisthesis is the anterior or posterior displacement of a vertebra of the vertebral column in relation to the vertebra below. In the lower region of the back where the lumbar vertebrae meet the sacrum, spondylolisthesis may occur more frequently. For example, at the L5-S1 level, the fifth lumbar vertebra may slip forward or in the anterior direction relative to the first level of the sacrum. Treatment for spondylolisthesis depends on the severity of the slippage. For severe cases, surgical correction is required.
Various systems and methods are known to alleviate and correct spondylolisthesis. For example, German Patent 41 27 303, filed Aug. 17, 1991 (also disclosed in European Patent No. 0528177, filed Jul. 16, 1992) to Aesculap AG, discloses such a device. Other devices include U.S. Pat. No. 6,565,568, filed Sep. 28, 2000 to Rogozinski and U.S. Pat. Pub. No. 2009/0216237, filed Jun. 30, 2006 to Frezal et al. However, some of these systems may be difficult to maneuver, attach, and remove from screw heads. Some of these systems may make it difficult to insert and secure fixation rods after correcting the slippage without removing portions of the systems.